Conventional fireplaces often draw combustion air from the room within the house in which they are situated and this is not only expensive because the air is usually preheated by the furnace system but also, with present day relatively well sealed houses, can cause an area of negative pressure to occur with the subsequent difficulties of smoke backing up from the fireplace. Also when the fireplace is used in a well sealed area, the air has to be drawn from such sources as sewer drain outlets (via the weeping tiles), clothes dryer outlets, and under certain circumstances, from the chimney of the conventional furnace. In conjunction with the furnace chimney, the quantity of air used by a fircely burning fireplace is sufficient that it can reverse the flow of the furnace chimney and draw the gases of combustion into the house with often dangerous results.
Another disadvantage of conventional fireplaces is that sparks and ashes often discharge therefrom onto carpets and floors and cold air enters the room through the fireplace chimney when same is not in use due to the inefficiency of conventional dampers.
The thermal efficiency of conventional fireplaces is usually extremely low and it is difficult to control the speed of consumption of wood and other products in the fireplace so that smoke produced by combustion at temperatures lower than optimum combustion (because of rapid fuel consumption) often result in undesirable and unnecessary pollution.